fix client crashing on empty passwords (regression)

src/main/java/eu/siacs/conversations/crypto/sasl/ScramMechanism.java

@@ -1,7 +1,6 @@
 package eu.siacs.conversations.crypto.sasl;
 
 import android.util.Base64;
-import android.util.Log;
 
 import com.google.common.base.CaseFormat;
 import com.google.common.base.Objects;
@@ -13,14 +12,32 @@ import java.nio.charset.Charset;
 import java.security.InvalidKeyException;
 import java.util.concurrent.ExecutionException;
 
+import javax.crypto.SecretKey;
 import javax.net.ssl.SSLSocket;
 
-import eu.siacs.conversations.Config;
 import eu.siacs.conversations.entities.Account;
 import eu.siacs.conversations.utils.CryptoHelper;
 
 abstract class ScramMechanism extends SaslMechanism {
 
+    public static final SecretKey EMPTY_KEY =
+            new SecretKey() {
+                @Override
+                public String getAlgorithm() {
+                    return "HMAC";
+                }
+
+                @Override
+                public String getFormat() {
+                    return "RAW";
+                }
+
+                @Override
+                public byte[] getEncoded() {
+                    return new byte[0];
+                }
+            };
+
     private static final byte[] CLIENT_KEY_BYTES = "Client Key".getBytes();
     private static final byte[] SERVER_KEY_BYTES = "Server Key".getBytes();
     private static final Cache<CacheKey, KeyPair> CACHE =

src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha1.java

@@ -15,7 +15,9 @@ public class ScramSha1 extends ScramMechanism {
 
     @Override
     protected HashFunction getHMac(final byte[] key) {
-        return Hashing.hmacSha1(key);
+        return (key == null || key.length == 0)
+                ? Hashing.hmacSha1(EMPTY_KEY)
+                : Hashing.hmacSha1(key);
     }
 
     @Override

src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha1Plus.java

@@ -15,7 +15,9 @@ public class ScramSha1Plus extends ScramPlusMechanism {
 
     @Override
     protected HashFunction getHMac(final byte[] key) {
-        return Hashing.hmacSha1(key);
+        return (key == null || key.length == 0)
+                ? Hashing.hmacSha1(EMPTY_KEY)
+                : Hashing.hmacSha1(key);
     }
 
     @Override

src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha256.java

@@ -19,7 +19,9 @@ public class ScramSha256 extends ScramMechanism {
 
     @Override
     protected HashFunction getHMac(final byte[] key) {
-        return Hashing.hmacSha256(key);
+        return (key == null || key.length == 0)
+                ? Hashing.hmacSha256(EMPTY_KEY)
+                : Hashing.hmacSha256(key);
     }
 
     @Override

src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha256Plus.java

@@ -15,7 +15,9 @@ public class ScramSha256Plus extends ScramPlusMechanism {
 
     @Override
     protected HashFunction getHMac(final byte[] key) {
-        return Hashing.hmacSha256(key);
+        return (key == null || key.length == 0)
+                ? Hashing.hmacSha256(EMPTY_KEY)
+                : Hashing.hmacSha256(key);
     }
 
     @Override

src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha512.java

@@ -19,7 +19,9 @@ public class ScramSha512 extends ScramMechanism {
 
     @Override
     protected HashFunction getHMac(final byte[] key) {
-        return Hashing.hmacSha512(key);
+        return (key == null || key.length == 0)
+                ? Hashing.hmacSha512(EMPTY_KEY)
+                : Hashing.hmacSha512(key);
     }
 
     @Override

src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha512Plus.java

@@ -15,7 +15,9 @@ public class ScramSha512Plus extends ScramPlusMechanism {
 
     @Override
     protected HashFunction getHMac(final byte[] key) {
-        return Hashing.hmacSha512(key);
+        return (key == null || key.length == 0)
+                ? Hashing.hmacSha512(EMPTY_KEY)
+                : Hashing.hmacSha512(key);
     }
 
     @Override